The study is an NSABP sponsored multi-center randomized trial to determine if tamoxifen in a daily dose of 20 mg reduces the risk of developing breast cancer compared to placebo. Women eligible for the study include women over the age of 60 or women 35 to 59 who have an estimated risk of developing breast cancer similar to that of a 60 year old woman. Participants take study pills for 5 years. We stopped enrolling women to the study in 1993; NSABP closed the study to enrollment in 1997. Over 50 women have been screened and 5 have been randomized. The majority of women refuse participation because of either potential side effects of tamoxifen or the wish to continue estrogen replacement therapy. One woman is now off the study after developing uterine cancer. Another woman went off the study because of side effects of the study pills. A third woman completed 5 years of taking study pills in November of 1997, and the last two women still taking study pills will stop taking the pills in February and July of 1998. Sally Brown, R.N., and Sue Markus, R.N., of the office of Dr. E. George Elias, will continue to collect reports of examinations, medical follow-up and history from all five women, at least through 1999. NSABP expects that enough information will be available to determine the preventive effects of Tamoxifen in 1999 or 2000.